Processing-dependent near-field radiative heat transfer at Au/SiC interfaces

Thermal annealing is a widely used thin-film processing technique for modifying interfacial optical losses and electronic scattering in metals. Here, we investigate how thermal annealing of gold thin films deposited on silicon carbide substrates influences interfacial near-field radiative heat transfer (NFRHT) across nanoscale vacuum gaps. Using experimentally measured dielectric functions for annealed and unannealed Au films, we evaluate the spectral and total radiative heat flux between Au/SiC interfaces within a fluctuational electrodynamics framework. We show that annealing-induced changes in the low-frequency dielectric losses of Au significantly alter evanescent electromagnetic coupling at the interface, leading to enhancements of up to 40% in the total NFRHT at separations of tens of nanometers. Mode-resolved analysis reveals that this enhancement originates from strengthened coupling of overdamped evanescent-surface modes, which are highly sensitive to thin-film processing and interfacial microstructure. These results demonstrate that standard thin-film processing can substantially modify near-field coupling through purely dielectric-property variations. The magnitude of this effect is comparable to variations often attributed to geometric uncertainty or gap calibration in experiments, highlighting the importance of material processing in the interpretation and control of NFRHT measurements.